Organic pollutants leaching from tire waste: Ecotoxicity implications for aquatic species

Tire-derived chemicals are emerging contaminants of environmental concern due to their continuous release from tire wear particles and their widespread occurrence in surface waters. This review synthesizes current knowledge on the environmental fate and ecotoxicological effects of key tire-associated compounds, with a focus on organic pollutants like N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine 6PPD, 6PPD-quinone (6PPD-Q), 1,3-diphenylguanidine (DPG), hexamethoxymethylmelamine (HMMM), and methyl isobutyl ketone (MIBK). These substances differ markedly in their physicochemical properties, transformation pathways, and toxicological profiles. A detailed literature review was conducted to identify peer-reviewed studies and safety data sheets addressing the occurrence, persistence, and biological impacts of these compounds across aquatic taxa. The analysis revealed that 6PPD-Q, a transformation product of the antioxidant 6PPD, is acutely toxic to sensitive fish species such as coho salmon (Oncorhynchus kisutch) at nanogram-per-liter concentrations, raising immediate ecotoxicological concerns. In contrast, DPG and HMMM show lower acute toxicity but are associated with sub-lethal effects under chronic exposure scenarios, including developmental and behavioral alterations. MIBK, though less persistent and more volatile, remains relevant due to its episodic presence in roadway runoff. The review highlights consistent patterns of species-specific sensitivity, with fish being particularly vulnerable, while significant data gaps persist for amphibians and for mixture toxicity. Emerging evidence of behavioral and developmental impacts underscores the potential for population-level consequences. The aim of this synthesis is to inform future research priorities and support the development of risk assessment frameworks and regulatory strategies to address the ecological risks posed by tire-derived contaminants in aquatic environments.